The present invention relates to an AT-cut quartz resonator, and more particularly to a thin and miniature AT-cut quartz resonator having excellent frequency-temperature characteristics of the vibration frequency, and high Q-values in which the vibration frequency of spurious vibration is sufficiently distant from that of the major thickness-shear vibration mode.
Conventionally, AT cut quartz resonators have been in popular use in telecommunication instruments or the like on account of their temperature characteristics, high Q-values and low equivalent series resistance.
The AT-cut quartz resonators which have been conventionally used have usually been disk shaped. The miniaturization of the AT-cut quartz resonators has been restricted since there are strong couplings between the major thickness-shear vibration and spurious vibrations, unless the dimensional ratio of the diameter to the thickness has been large, and the Q-values and the frequency-temperature characteristics of these quartz resonators are very poor.
On the other hand, a rectangular AT-cut resonator has been proposed since it is advantageous for miniaturization. According to the Japanese Opened Pat. Nos. 100991/74 and 97394/76, the length-to-thickness ratio l/t of a quartz crystal plate should be more than 30. In case the major surfaces (X-Z' planes) and the side surfaces (X-Y' planes) of the quartz crystal plate meet substantially at right angles, the temperature of the inflection point of the frequency-temperature curve becomes gradually higher than that of the AT-cut quartz resonator of an infinite plate, if the width-to-thickness ratio w/t of the quartz crystal plate becomes less than eight. When w/t is three, the temperature of the inflection point is substantially 40.degree., consequently the quartz crystal plate is not suitable for use at room temperature. An AT-cut quartz resonator having a cubic temperature curve having the temperature of the inflection point at room temperature, preferably at 20.degree. C., is suitable for use in a wrist watch and a portable electronic device, though such has not been invented yet.
Accordingly, it is an object of the present invention to provide a new AT-cut quartz resonator of sufficiently miniature size to be incorporated into a wrist watch, and of high Q-values and of low equivalent series resistance and having the temperature of the inflection point of the frequency-temperature curve near 20.degree. C. for practical use, and further having the spurious vibration frequencies differ from the major thickness-shear vibration frequency and for which mass production and accurate finishing is permitted.